A technique of transmitting the service information through the multiplex operation using blank periods among the broadcasting waves has been used extensively. Particularly, in recent years, a service to provide information related to a program being on the air or other kinds of information, such as news and weather forecast, has become popular and known as a so-called visible radio.
The FM teletext multiplex broadcasting roughly includes two kinds: one is a free broadcasting in which anyone can use information, such as news and weather forecast, once he has purchased an adaptable receiver terminal; and the other is a restricted broadcasting in which only those who have purchased special-purpose receiver terminals and paid the reception charge can use the information.
A service identification is appended to the service information provided through the FM teletext multiplex broadcasting. A general radio receiver used as the visible radio is arranged to decode only the service information appended with a free broadcasting service identification so as to display the text, and not to capture the rest of the service information appended with a restricted broadcasting service identification. In contrast, the receiver terminal for the restricted broadcasting is arranged to decode the service information appended with all the operable service identifications so as to display the text. The receiver terminal of this type may be arranged to also display the text of the service information provided through the free broadcasting.
In the restricted broadcasting, anyone who wishes to use the service information is requested to purchase the special-purpose receiver terminal and pay the reception charge, and it must be arranged in such a manner that only the user who has paid the reception charge and signed up the reception contract is authorized to use the service information.
In case of VICS (Vehicle Information Communication System) which has been already provided as a restricted broadcasting using the FM teletext multiplex broadcasting, the price of a vehicle navigation device includes the reception contract charge. Thus, once the user has purchased the vehicle navigation device, he can receive the information without any additional charge.
However, in this charging system, a reception authorization period depends on the usable period of the receiver terminal or the operating life of the product. Thus, the benefits depends on the usable period or the operating life of the product the user has purchased, and therefore, the users do not necessarily appreciate the benefits equally. In addition, if the receiver terminal is upgraded to have a longer operating life, the user replaces the receiver terminal less frequently, which causes a falloff of revenues from the reception charge. Further, this charging system is not applicable in case that each user does not receive the same service information, but different kinds of service information.
Thus, to enable only the users who have duly paid the reception charge periodically to receive the service information commensurate with the reception charge, it is necessary to periodically reset the contents of the receivable services and the reception authorization period for each user or each receiver terminal.
A typical conventional technique to meet such a demand is disclosed in, for example, Japanese Laid-open Patent Application Nos. 149027/1996 (Tokukaihei 8-149027) and 186549/1996 (Tokukaihei 8-186549). In Japanese Laid-open Patent Application No. 149027/1996, after the user paid the reception charge through the financial institutions, a provider of the restricted broadcasting, such as an FM broadcast station, transmits an individual ID code assigned to each user and a pay ID code used as encoding information to enable the user to receive the charged service information on the multiplex broadcasting waves. Each receiver terminal is arranged to detect the individual ID code that matches with its own ID code, capture the pay ID code following the individual ID code, and display the texts of the transmitted service information after confirming the same pay ID code is set in itself.
In the above Japanese Laid-open Patent Application No. 186549/1996 (Tokukaihei 8-186549), the user purchases a prepaid IC card, and the receiver terminal is arranged to display the texts of the service information in accordance with the reception control information, such as the validity and service contents, stored in the IC card inserted therein.
In the technique disclosed in above Japanese Laid-open Patent Application No. 149027/1996 (Tokukaihei 8-149027), a reception authorization code is transmitted from the broadcast station in the similar manner as the widely spread satellite broadcasting using broadcast satellites or communications satellites. For this reason, the receiver terminal must include a circuit to decode the reception authorization code. Thus, there is a problem in that the arrangement of the receiver terminal becomes complicated, thereby increasing the cost. Also, since the reception authorization code must be transmitted to each receiver terminal within a limited transmission capacity of the broadcasting waves, the technique may not be used if the number of the receiver terminals exceeds a certain level. In addition, an amount of information increases as program service is upgraded. But on the other hand, the service information is repeatedly transmitted to eliminate adverse effects, such as noise. Thus, there is a problem in that the number of the users or the kinds of services can not be increased under these conditions. This problem is especially obvious in the FM teletext multiplex broadcasting having a very small transmission capacity (16 kbps) compared with the satellite broadcasting. Further, the user can not receive the service information unless he receives the reception authorization code. Thus, before the actual reception of the service information starts, the user has to keep the receiver terminal turned ON for a predetermined time during a contract update unit period, for example, a month, so that the receiver terminal is in a reception state when its own individual ID code and pay ID code are transmitted.
In the case of the arrangement of above Japanese Laid-open Patent Application No. 186549/1996 (Tokukaihei 8-186549) using the prepaid IC card or the like, the receiver terminal must include interface mechanism for reading/writing the information from/in the prepaid card or the like. Thus, there is a problem in that the arrangement becomes complicated, and not only the cost but also the power consumption increases. Although the prepaid cards or the like are readily available as they are sold at convenience stores, electrical appliance stores, etc., the reception charge increases because the producing costs of the cards and the sales charge are added thereto. Also, the medium compatible with many types of receiver terminals, such as the prepaid card, may be forged or altered no matter how well the security system is improved except for the medium employing an exceptional arrangement such that automatically destroys the memory content when the validity expires as disclosed in Japanese Laid-open Patent Application No. 256071/1996 (Tokukaihei 8-256071).